Integrated Design Of Vibration Isolation And Attitude Control For High Resolution Remote Sensing Satellites

The space camera onboard the high resolution remote sensing satellite is extremelysensitive to disturbances, which can degrade the performance by resulting in blurred ordistorted image. To reduce the line-of-sight jitter caused by disturbances, passiveisolators can be added between the satellite bus and the reaction wheel, or between thesatellite bus and the space camera. To achieve better disturbance attenuation, isolatorswith lower cut-off frequencies should be used, which, however, may degrade theattitude control performance. This paper will focused on finding the lower limit of theisolation frequency with its impacts on the attitude control performance taken intoaccount. If the requirement for isolation performance cannot be satisfied, an integrateddesign of the isolator and attitude control will be performed to achieve better vibrationattenuation.The integrated modeling of structures-controls-optics is studied, which is necessaryto evaluate the impact of disturbances on the image quality. The disturbance generatedby the reaction wheel is characterized and demonstrated through disturbance tests. Acomponent mode synthesis method is studied for structures connected with isolators,which can reduce the eigenvalue re-analysis costs when tuning the isolator parameters.The image formation principles, the optical sensitivity and the performance metricsderived from the modulation transfer function are introdued which are useful inevaluating the impact of disturbances on the image.The selection of wheel isolation parameters is studied with the impact on theattitude control performance taken into account. The motion of equation of the reactionwheel mounted on an isolator is derived and the disturbance transmissibilities in6degree of freedoms are analysed. The precession and nutation phenomena of a wheel onan isolator as well as the wheel percession excited by the base motion are studied. It isshown that the lower limit of the frequency and damping ratio of the wheel isolator ismainly determined by the required precession decay time.The integrated design method of camera isolation and attitude control is studied.The non-collocated control problem induced by the camera isolation is investigated andan analytical stability condition is derived, which indicates that the settling time of theisolator should be shorter than the controller to ensure the system stability. A loop phase based analysis method is proposed and applied in the controls-structures interactionstudy, which shows that it is the negative damping added to the sturctural mode by thecontrol loop that makes the non-collocated control system easily be destablized. Anintegrated design method of camera isolation and attitude control is studied, which canachieve better disturbance attenuation compared to separate design.A design method based on optimization is proposed to help determine theparameters of vibration isolators. A control law modification strategy is added to theoptimization process to perform integrated design of the vibration isolator and attitudecontrol. Results show that a combination of wheel isolation, low frequency cameraisolation and the corresponding control law modification can result in optimaldisturbance attenuation while ensuring the attitude control performance.